Not applicable.
This invention relates generally to electrospray devices, and more particularly to an improved electrospray ion source assembly.
Electrospray (ES) is a method of producing highly charged droplets and gas phase ions. A particularly useful application for electrospray is the production of gas phase ions from analytes in liquid solutions delivered by methods such as high pressure liquid chromatography, capillary electrophoresis or capillary electrochromatography to a system for detection and analysis, such as a mass spectrometer (MS).
The electrospray process generally includes flowing an analyte liquid into an electrospray ion source comprising a small tube or capillary which is maintained at a high voltage in absolute value terms, with respect to a nearby surface. The small tube or capillary functions as an emitter electrode. In a typical ES-MS system, a solution containing analytes of interest is pumped through the emitter electrode and sprayed towards the remotely located orifice plate of the mass spectrometer. In this arrangement, the orifice plate functions as the counter electrode.
Under the influence of the electric field between the emitter electrode and the orifice plate, ions in solution that are of the same polarity as the voltage applied to the ES capillary buildup an excess charge at the surface of the liquid exiting the emitter until a point is reached where the Coulombic forces are sufficient to overcome the surface tension of the liquid. At this point, droplets enriched in ions of this polarity are emitted from the capillary and drift toward the counter electrode. This process produces a quasi-continuous steady-state electrical current.
The inability to completely separate positive ions from negative ions in solution is the fundamental limit to generation of the maximum gas-phase ion production during ES ionization. Ideally, complete separation of positive and negative ions would produce maximum gas-phase ion production. However, conventional ES ion sources provide charge separation of no better than about 50% (1).
An electrospray ion source includes a chamber which provides a channel region therein, the channel including at least one inlet for directing a solution into the channel and at least a first and a second outlet for transmitting the solution or derivatives therefrom out from the channel. A structure for separating ions in the solution separates the solution into at least a first and a second flow stream portion. The first flow stream portion is enriched in negative ions and the second flow stream portion is enriched in positive ions. The first flow stream portion exits the chamber through the first outlet while the second flow stream portion exits the chamber through the second outlet. Accordingly, the invention can be used to simultaneously generate gas phase ions of opposite polarity from a given sample.
The structure for separating ions can include a device for generating an electrical field in the channel. The electrical field is preferably oriented in a direction substantially orthogonal to a flow direction of the solution in the channel. The device for generating an electrical field can comprise at least one capacitor, the capacitor including at least two electrodes, the electrodes positioned on substantially opposite sides of the channel. The structure for separating ions can be adapted to provide a time varying electromagnetic field in the channel.
The structure for separating ions can comprise a device for generating a magnetic field in the channel. The device for generating a magnetic field can be an electromagnet.
The electrospray source can be microfabricated, such as on a chip. In this embodiment, the channel includes at least a first and second integrated electrode.
An electrospray system can include a plurality of the electrospray ion sources of claim 1. In this embodiment, at least two of the plurality of electrospray ion sources are connected in series. This arrangement can be used to further increase charge separation efficiency, if desired.
An electrospray method for generating at least one charged fluid includes the steps of providing an electrospray ion source, the electrospray ion source including at least one input and at least a first output and a second output. Fluid is flowed through the input into the electrospray ion source. The fluid is then separated into a positively charged fluid stream portion and a negatively charged fluid stream portion, wherein the positively charged fluid stream portion is emitted from the first output and the negatively charged fluid stream portion is emitted from the second output. The separating step can include applying at least one electromagnetic field to the fluid in the electrospray ion source. The electromagnetic field can be a time varying electromagnetic field.
The electromagnetic field can be generated between the plates of a capacitor. The method can simultaneously provide at least two gas phase ion stream portions having opposite polarity, a first polarity emitted from the first output and the other polarity emitted from the second output.